The present invention relates to a bistable straight line motion actuator mechanism of a type suitable for actuating a poppet valve in an internal combustion engine. More particularly, the invention relates to an electronically controlled, pneumatically powered actuator which is hydraulically latched.
An actuator mechanism of the above described type is disclosed in U.S. Pat. No. 5,022,359, which patent is incorporated herein by reference. This patent gives a thorough discussion of prior art actuators, particularly pneumatically powered actuators with energy storage schemes for converting kinetic energy to potential energy using compressed air. Virtually all of the prior art actuators discussed in the patent use some type of magnetic latching for holding the actuator in one of two stable positions.
U.S. Pat. No. 5,022,359 discloses a mechanism which uses a low air pressure (about 10 psi) to hold a working piston in its first stable position (engine valve closed). When a magnetic control valve is electronically switched, high air pressure (about 100 psi) drives the piston toward its second stable position compressing the air in front of it. This motion admits hydraulic fluid to an expansion chamber via a ball check. When the piston reaches its second stable position, the control valve has returned to its initial state, cutting off the air supply, and the compressed air behind the piston is released to atmosphere. The air in front of the piston is fully compressed, but the ball check closes and hydraulic fluid in the expansion chamber prevents motion back toward the first stable position, thereby maintaining the engine valve open. At the conclusion of the valve dwell, an electronically controlled magnetic plunger forces the ball check open, and the compressed air (stored potential energy) forces the piston back toward its first stable position. Air is compressed in front of the moving piston to dampen its motion, but this air is released just as the piston reaches its first stable position.
The actuator mechanism disclosed in U.S. Pat. No. 5,022,359 represents an improvement over the prior art insofar as externally derived propulsion air is used only to open the engine valve, and not to close it. The compressed air consumed is therefore decreased to about half the air consumed in prior pneumatically powered systems. However, two separately controlled magnetic mechanisms, one for the air control valve and one for the plunger to release the ball check, are required. Since the air control valve is rather large, a large electromagnetic latch is required. Further, due to the time required to pressurize the piston with air, after the control valve is switched, the response time is slow and not suited to use at high RPM.